Connotation and evaluation technique of geological integrity of UGSs in oil/gas fields

Abstract

Whole-life-cycle integrity management of underground gas storages (UGSs) has been an important link to ensure its long-term safe and efficient operation. At present, the integrity of UGSs in oil/gas fields and its evaluation techniques focus on surface facilities and injection/withdrawal wells, but its geological integrity lacks clear definition and evaluation object and systematic evaluation techniques. In this paper, relevant research achievements were firstly summarized. Then, the concept of geological integrity with the gas-storage geological body as the evaluation object was put forward, and the evaluation system for the geological integrity of such UGSs was established. Finally, UGS geological integrity evaluation was carried out with the Hutubi Underground Gas Storage in Xinjiang as an example. And the following research results were obtained. First, UGS geological integrity is defined as the integrity degree of each component of a gas-storage geological body to meet operation requirements and fulfill seasonal and emergency peak shaving safely and economically during the operation of a UGS. Its connotation is that reservoir of geological body, caprock, fault and trap can supply the customers with gas continuously and stably and ensure the safe operation of the UGS in its service life. And its core lies in keeping the reliability, safety and economy of natural gas storage in the service life of a UGS. Second, the geological integrity evaluation system is composed of four evaluation techniques, including trap effectiveness, caprock integrity, fault stability and reservoir stability. Third, the evaluation results show that the Hutubi Underground Gas Storage has the potential of peak-shaving capacity enhancement by increasing the maximum operation pressure. In conclusion, the establishment of the geological integrity evaluation system for such UGSs improves the UGS integrity evaluation technique system and plays an instructive and practical role in ensuring the long-term safe and efficient operation of UGSs, increasing the maximum operation pressure and improving the peak shaving capacity.